Personal assistant modules are software processes installed on computing devices such as smart phones, tablets, vehicle navigation systems, smart watches, as well as general purpose computing devices (e.g., desktops, laptops) to provide user-friendly interfaces for users to issue natural language commands. Users often issue natural language commands using their voices, but personal assistant modules may respond to other modalities as well, such as various forms of textual and/or image input. Users may communicate with personal assistant modules and/or each other textually via message exchange threads implemented using various technologies, such as text messaging, online chat (e.g., instant messenger, Internet relay chat, etc.), social network threads, interactive voice response, and so forth. The ongoing message exchange thread is typically limited to text (e.g., typed or generated from voice input) or other data such as pictures that users deliberately and explicitly incorporate into the message exchange thread.